Here are some shots of my sky system. The clouds are 100% generated and
lighted on the GPU. I use 8 octaves Perlin noise, and the lighting is
integrated on the GPU using a ray-tracing technique that I described in
details in the upcoming Game Programming Gems 5 book available in March
2005. The clouds are fully dynamic, I can control the speed of
deformation, the speed and direction of the wind, the density over the
entire sky, etc.